Logic lessons don't always go with life.

Sungmin will do everything just to prove Kyuhyun is not genius.

Kyuhyun expresses his feelings through writing letters to Sungmin, telling him he cannot move on.

Endless means forever.

Sungmin was born in a date which only happens in every four year. He considers himself as unlucky, but what if he's not really unfortunate after all?

Kyuhyun prioritizes his music more than Sungmin. Isn't Sungmin enough to be his 'music'?